CN1711310A - Process and apparatus for depositing plasma coating onto a container - Google Patents

Abstract

The present invention describes a method and an apparatus for plasma coating the inside surface of a container to provide an effective barrier against gas transmission. The method provides a way to deposit rapidly and uniformly very thin and nearly defect-free layers of polyorganosiloxane and silicon oxide on the inner surface of a container to achieve more than an order of magnitude increase in barrier properties.

Description

Method and apparatus for depositing a plasma coating in a vessel

The present invention relates to a method and apparatus for depositing a plasma-formed coating in a container, more particularly on the inner surface of a container, preferably in a plastic container.

For many years, plastic containers have been used to package carbonated and non-carbonated beverages. Consumers prefer to use plastics such as polyethylene terephthalate (PET) or polypropylene (PP) because they are resistant to cracking, lightweight and transparent. Unfortunately, the relatively high permeability to oxygen and carbon dioxide limits the shelf life of beverages packaged in plastic.

Efforts to treat plastic containers to render them relatively low oxygen and carbon dioxide permeability are known. For example, Laurent et al. (WO 9917333) describe the use of plasma enhanced chemical vapor deposition (PECVD) to coat the inner surface of plastic containers with a layer of _SiOx . In general, _SiOx coatings provide an effective barrier to gas permeation, however, for plastic containers, _SiOx is not sufficient to form an effective barrier to gas permeation.

In US Patent No. 5,641,559, Namiki describes the deposition of a plasma polymerized silicon compound followed by a layer _{of SiOx} on the outer surface of PET and PP bottles. The thickness of the polymeric silicon compound is 0.01-0.1 μm, and the thickness of the SiO _x layer is 0.03-0.2 μm. Although Namiki discloses that the combination of a plasma-polymerized silicon compound and a _SiOx layer (where x is 1.5-2.0) provides better barrier properties than either layer alone, the total deposition time of the coating is between 15 minutes or so, which is impractical for commercial applications. Furthermore, the method described by Namiki is disadvantageous in that too much plasma-polymerized monomer is deposited outside the desired substrate. This unwanted deposition results in too low a precursor-to-coating conversion, causing contamination and fouling of equipment, as well as non-uniform substrate coatings.

Accordingly, it would be desirable to develop a method for uniformly and rapidly coating containers, especially plastic containers, which provides an effective barrier to gas penetration and reduces contamination.

The present invention aims to solve the problems of the prior art by providing a method of preparing a protective barrier for a container having an inner surface, the method comprising the following steps: a) subjecting the first plasma polymerizing an organosilicon compound under polymerization conditions to deposit a polyorganosiloxane layer of uniform thickness on the inner surface of the container; and b) under partial vacuum, subjecting a second organosilicon compound to polymerization conditions Plasma polymerisation to deposit silicon oxide layers superimposed on the same or different polyorganosiloxane layers.

In another aspect, the present invention is an improved apparatus for depositing a plasma-formed coating on a surface of a container having: a) an outer conductive resonant cylinder having a cavity, an inner side and an outer side; b ) a generator that can provide an electromagnetic field in the microwave region and is connected to the outside of the resonant cavity; c) a waveguide located between the outer conductive resonant cylinder and the generator, which can directly guide the microwave to the outer conductive resonant cylinder inside; d) a microwave-permeable cylindrical tube in the outer conductive resonant cylinder, which is closed at one end and open at the other end, allowing access to the container; e) at least one conductive plate in the resonant cavity and e) a cap for opening one end; wherein the improvement includes a syringe secured to the cap that is porous, coaxial, longitudinally reciprocating, or rotates about a longitudinal axis, or a combination thereof, the A syringe can be inserted into the container such that it extends at least partially into the container.

FIG. 1 is an explanatory diagram of an apparatus for coating the inside of a container.

The method of the invention is advantageously carried out using the apparatus described in WO 0066804, although this is not the only one, made with some modifications to FIG. 1 . The device 10 has an outer conductive resonant cavity 12, which is preferably cylindrical (also referred to as outer conductive resonant cylinder with cavity). Apparatus 10 includes a generator 14 connected to the outside of cavity 12 . This generator 14 is capable of providing an electromagnetic field in the microwave region, more specifically a field corresponding to a frequency of 2.45 GHz. The generator 14 is installed on the box 13 on the outside of the resonant cavity 12, and the electromagnetic radiation it provides is fully perpendicular to the axis A1, extends along the radius of the resonant cavity 12, and is exposed through a window located inside the resonant cavity 12 The outgoing waveguide 15 is brought into the resonant cavity 12.

The tube 16 is a microwave-permeable hollow cylinder inside the resonator, closed at one end by a wall 26 and open at the other end to allow access to the container to be treated by PECVD. Container 24 may be fabricated from any non-conductive material, including glass, ceramics, composites, and plastics. Container 24 is preferably plastic, such as polyalkylene terephthalates, including polyethylene terephthalate and polybutylene terephthalate; polyolefins, including polypropylene and polyethylene Polycarbonate; Polyvinyl chloride; Polyethylene naphthalate; Polyvinylidene chloride; Polyamides, including nylon; Polystyrene; Polyurethane; Epoxy resins; Acrylic resins, including polymethylmethacrylate; and polylactic acid.

The open end of the tube 16 is then sealed by the cap 20 so that a partial vacuum can be drawn in the space defined by the tube 16 , establishing a low partial pressure inside the container 24 . The container 24 is held at the neck on the holder 22 of the container 24 . A partial vacuum is advantageously applied to both the inside and outside of the container 24 to avoid deformation of the container 24 by subjecting the container 24 to a pressure differential that is too large. The partial vacuum is different inside and outside the vessel, where a partial vacuum is maintained so that no plasma is formed outside the vessel 24 where deposition is not desired. Preferably, the partial vacuum inside the container 24 is maintained at 20-200 μar, while the partial vacuum outside the container 24 is evacuated to 20-100 mbar, or lower than 10 μbar.

The cap 20 cooperates with a syringe 27 secured to the container 24 so as to protrude at least partially into the container 27 to introduce the active fluid containing the active monomer and carrier. The syringe 27 can be designed, for example, to be porous, open, longitudinally reciprocating, rotating, coaxial, and combinations thereof. As used herein, the word "porous" is used in its traditional sense, meaning that it has holes, and also generally refers to any gas-permeable passage, which may include one or more slits. A preferred embodiment of the syringe 27 is an open porous syringe, more preferably an open, graded porosity, i.e. a syringe with different levels of porosity, which preferably extends substantially the entire length of the container . The pore size of the injector 27 increases towards the bottom of the container 24 to optimize the flow uniformity of the reactive precursor gas on the inner surface of the container 24 . Figure 1 illustrates this difference in porosity with varying degrees of shading, which shows that the porosity in the upper third 27a of the syringe is lower than the porosity in the middle third 27b of the syringe, which - 27b has a lower porosity than the lower third of the syringe 27c. The porosity of the syringe 27 is generally 0.5 μm to 1 mm. Grading, however, can take various forms, from the illustrated stepwise to truly continuous. The diameter of the cross-section of the syringe 27 can vary from just below the inner diameter of the narrowest part of the container 24 (typically starting at 40 mm) to 1 mm.

Apparatus 10 also includes at least one conductive plate in the cavity for tuning the geometry of the cavity to control the plasma distribution in vessel 24 . More preferably, though not required, as illustrated in FIG. The conductive plates 28 and 30 are moved relative to each other so that they are attached axially on either side of the tube 16 through which the waveguide 15 leads into the cavity 12 . The design of the conductive plates 28 and 30 enables the modulation of the electromagnetic field to ignite and maintain the plasma during deposition. The position of conductive plates 28 and 30 can be adjusted using slide bars 32 and 34 .

Deposition of polyorganosiloxane and SiOx layers can be achieved as follows. A gas mixture comprising a balance gas and a working gas (collectively referred to as the total gas mixture) is passed through injector 27 at a concentration and power density and for a time sufficient to form a coating having the desired gas barrier properties.

As used herein, the term "working gas" refers to a reactive substance, which may or may not be a gas, at standard temperature and pressure, capable of polymerizing on a substrate to form a coating. Examples of suitable working gases include organosilicon compounds such as silanes, siloxanes and silazanes. Examples of silanes include tetramethylsilane, trimethylsilane, dimethylsilane, methylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxy Diethoxysilane, Diethoxydimethylsilane, Methyltriethoxysilane, Triethoxyvinylsilane, Tetraethoxysilane (also known as Tetraethyl Orthosilicate, or TEOS), Dimethyl Oxymethylphenylsilane, phenyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloylpropyltrimethoxysilane, diethoxymethylphenylsilane, Tris(2-methoxyethoxy)vinylsilane, phenyltriethoxysilane and dimethoxydiphenylsilane. Examples of siloxanes include tetramethyldisiloxane, hexamethyldisiloxane and octamethyltrisiloxane. Examples of silazanes include hexamethylsilazane and tetramethylsilazane. Siloxanes are the preferred working gases, with tetramethyldisiloxane (TMDSO) being particularly preferred.

As used herein, the term "balance gas" is the reactive or non-reactive gas that carries the working gas through the electrodes and ultimately onto the substrate. Examples of suitable balance gases include air, _O2 , _CO2 , NO, _N2O , and combinations thereof. Oxygen ( _O2 ) is the preferred balance gas.

In the first plasma polymerization step, in an oxygen-enriched atmosphere, the first organosilicon compound is plasma-polymerized on the inner surface of the container, and the inner surface of the container can be surface-modified in advance, such as roughening, cross-linking Or surface oxidation, or no surface modification in advance. As used herein, the term "oxygen-enriched atmosphere" means that the equilibrium gas contains at least 20% oxygen, more preferably at least 50% oxygen. Thus, for the purposes of this invention, air is a suitable equilibrium gas, but _N2 is not.

The mass of the polyorganosiloxane layer is substantially independent of this percentage until the equilibrium gas constitutes a mole percent of the total gas mixture up to 80 mole percent, at which point the quality of the layer deteriorates substantially. The power density of the plasma used to prepare the polyorganosiloxane layer is preferably greater than 10MJ/kg, more preferably greater than 20MJ/kg, most preferably greater than 30MJ/kg; preferably less than 1,000MJ/kg, more preferably less than 500MJ/kg, most preferably Preferably less than 300 MJ/kg.

In this first step, the plasma preferably lasts less than 5 seconds, more preferably less than 2 seconds, most preferably less than 1 second; and preferably longer than 0.1 seconds, more preferably longer than 0.2 seconds, to form a thickness preferably less than 500 Å, more preferably less than 200 Å, most preferably less than 100 Å; preferably greater than 25 Å, more preferably greater than 50 Å polyorganosiloxane layer.

The first plasma polymerisation step is preferably carried out at a deposition rate of less than 500 Å/sec, more preferably less than 200 Å/sec, preferably greater than 50 Å/sec, more preferably greater than 100 Å/sec.

The preferred chemical composition of the polyorganosiloxane layer is SiO _x C _y H _z , where x is 1.0-2.4, y is 0.2-2.4, and z is greater than or equal to 0, more preferably not greater than 4.

In the second plasma polymerization step, the second organosilicon compound, which may be the same as or different from the first organosilicon compound, is plasma-polymerized on the polyorganosiloxane layer as described above to form a silicon oxide layer, or it may be different from the first organosilicon compound. polyorganosiloxane layer. In other words, more than one polyorganosiloxane layer having a different chemical composition is possible and sometimes advantageous. The silicon oxide layer is preferably a SiO _x layer, where x is 1.5-2.0.

For the second plasma polymerisation step, the molar ratio of balance gas to gas mixture is preferably stoichiometric for balance gas and working gas. For example, when the balance gas is oxygen and the working gas is TMDSO, the preferred molar ratio of the balance gas to the total gas is 85-95%. The power density of the plasma used to prepare the silicon oxide layer is preferably greater than 10MJ/kg, more preferably greater than 20MJ/kg, most preferably greater than 30MJ/kg; preferably less than 500MJ/kg, more preferably less than 300MJ/kg.

In this second step, the plasma lasts preferably less than 10 seconds, more preferably less than 5 seconds, preferably longer than 1 second, to form a thickness of less than 500 Å, more preferably less than 300 Å, most preferably less than 200 Å, preferably greater than 50 Å, A silicon oxide coating greater than 100 Å is more preferred.

The second plasma polymerisation step is preferably carried out at a deposition rate of less than 500 Å/sec, more preferably less than 200 Å/sec, preferably greater than 50 Å/sec, more preferably greater than 100 Å/sec.

The total thickness of the first plasma polymerized layer and the second plasma polymerized layer is preferably less than 1,000 Å, more preferably less than 500 Å, more preferably less than 400 Å, most preferably less than 300 Å, preferably greater than 100 Å. The total deposition time for plasma polymerization (ie the deposition time for the first and second layers) is preferably less than 20 seconds, more preferably less than 10 seconds, most preferably less than 5 seconds.

It was unexpectedly found that a very thin coating of uniform thickness can be rapidly deposited on the inner surface of a container to form a barrier to the permeation of small molecules such as _O2 and _CO2 . As used herein, the term "uniform thickness" means that the thickness of the coating varies by less than 25% over the entire coating area. Preferably the coating is substantially free of cracks or pinholes. Preferably the Barrier Improvement Factor (BIF, the ratio of the transmission rate of an untreated bottle to a treated bottle for a specific gas) is at least 10, more preferably at least 20.

The following examples are for illustrative purposes and do not limit the scope of the invention.

Example - Preparation of plasma coatings on PET bottles

An apparatus as shown in FIG. 1 is used in this example. In this embodiment, container 24 is a 500 mL PET bottle suitable for carbonated beverages. The vial 24 is inserted into the tube 16 located in the resonant cavity 12 . The cap 12 is fitted with an open stepped multi-hole syringe 27 secured to the bottle so that the syringe 27 protrudes 1 cm from the bottom of the bottle. The syringe was fabricated by welding together three 2.5" (6.3cm) long sections of porous hollow stainless steel tubing (0.25" (0.64cm) OD, 0.16" (0.41cm) ID), each with a different porosity, A single 7.5" (19 cm) stepped syringe was formed as illustrated in Figure 1 . The pore size of the upper third 27a of the syringe is 20 μm, the pore size of the middle third 27b of the syringe is 30 μm, and the pore size of the lower third 27c of the syringe is 50 μm (porous tubing purchased from Mott).

A partial vacuum is established both inside and outside the bottle 24 . The outside of the bottle 24 was kept at 80 mbar, while its inside was initially kept at 10 μbars. A layer of organosiloxane was uniformly deposited on the inner surface of the bottle 24 as follows. TMDSO and _O2 were flowed together through syringe 27 at a rate of 10 sccm, thereby raising the partial pressure inside the vessel. Once the partial pressure reaches 40μbars (generally less than 1 second), apply a power of 150W (equivalent to a power density of 120MJ/kg) for 0.5 seconds to form an organosiloxane layer with a thickness of 50 Å.

A _SiOx layer was uniformly deposited on the organosiloxane layer according to the following method. TMDSO and O ₂ flow together through the syringe 27 at flow rates of 10 sccm and 80 sccm, respectively, thereby raising the partial pressure inside the bottle 24 . Once the partial pressure reaches 60μbars (generally less than 1 second), a power of 350W (equivalent to a power density of 120MJ/kg) is applied for 3.0 seconds to form a SiO _x layer with a thickness of 150 Å.

Barrier properties are expressed by the barrier improvement factor (BIF), which expresses the ratio of the oxygen transmission rate of the uncoated bottle to the oxygen transmission rate of the coated bottle. The BIF was 27 as measured using an Oxtran 2/20 oxygen permeation device (available from Mocon). This corresponds to an oxygen transmission rate of 0.0017 cm ³ /bottle/day.

Claims (9)

1. be used to the container with internal surface to prepare the method for protecting barrier layer, this method comprises the steps:

A) under partial vacuum and in the atmosphere of oxygen enrichment, make first silicoorganic compound under polymerizing condition, carry out plasma polymerization with the uniform organopolysiloxane layer of deposition one layer thickness on inner surface of container; And

B) under partial vacuum, make second silicoorganic compound under polymerizing condition, carry out plasma polymerization and be stacked and placed on the uniform silicon oxide layer of thickness on the identical or different organopolysiloxane layer with deposition.

2. method according to claim 1 is wherein carried out the plasma polymerization step with the so concentration and the time of the power density and first and second silicoorganic compound, makes the total thickness of organopolysiloxane and silicon oxide layer less than 400 .

3. method according to claim 1 and 2, wherein with greater than 100 /sec, implement the first plasma polymerization step less than the sedimentation velocity of 200 /sec, implement the second plasma polymerization step under the sedimentation velocity of 60 /sec being not less than 30 /sec and being not more than, and wherein total depositing time of plasma polymerization is not more than 10 seconds.

4. according to the arbitrary described method of claim 1-3, wherein use general formula SiO _xC _yH _zThe expression organopolysiloxane, wherein x is 1.0～2.4, y is 0.2～2.4, and z is not more than 4, uses SiO _xThe expression silicon oxide layer, wherein x is 1.5～2.0, and wherein this container contains the plastics of polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene or poly(lactic acid).

5. according to the arbitrary described method of claim 1-4, wherein send into the oxygen and first and second silicoorganic compound by syringe reciprocal, that rotate or co-axial or their combinations porous, opening, vertical.

6. method according to claim 5, wherein send into the oxygen and first and second silicoorganic compound by being arranged in container and being stretched over almost the classifying porous syringe of opening of entire container length, wherein porosity increases being staged or continous way on the direction of container bottom.

7. method according to claim 6, the inboard of this container and outside retaining part vacuum all wherein, wherein the partial vacuum of container inside is extremely about 200 μ bar of about 20 μ bar, and the partial vacuum of outside of containers is that 20mbar is to about 100mbar or less than 10 μ bar.

8. the equipment of the coating that deposition plasma forms on a kind of improved surface that is used at container, this equipment has:

A) have chamber, inboard and the outer outer conduction resonant cylindrical shell of surveying;

B) electric organ that can electromagnetic field is provided in the microwave region and link to each other with the outer survey of resonator cavity;

C) outside waveguide between conduction resonant cylindrical shell and the electric organ, the inboard of outer conduction resonant cylindrical shell can be directly guided microwave in this waveguide;

D) be arranged in the cylindrical tube of outer conduction resonant cylindrical shell to microwave, this pipe is at one end closed, opens at the other end, makes it possible to feed in the container;

E) be arranged at least one conducting plates of resonator cavity; With

F) be used to open the lid of an end;

Wherein improvements comprise the syringe that is fixed in lid, this syringe be porous, co-axial, vertically reciprocal or rotate round the longitudinal axis, perhaps their combination, this syringe can insert in the container, makes it have at least part to extend in the container.

9. equipment according to claim 8, wherein syringe is classifying porous and opening, and wherein porosity is being staged or continuous mode increases in the direction towards the injector orifice part.

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